Humans show considerable variation in trichromatic color vision, which is the presence of three retinal cones tuned to different wavelengths. Approximately 8 percent of Caucasian males, for example, show color vision abnormalities. This variation stands in contrast to the remarkable uniformity of vision found in Old World monkeys, apes, and the Neotropical genus of howling monkeys. Variations in these populations are extremely rare and, at the moment, it is unclear why trichromacy twice evolved so similarly in primates but in no other known mammal. The hypothesis that young, colored leaves may have selected for trichromatic color vision in primates has recently received support. Among mammals, however, molecular evidence on the color vision of specialized, non-primate frugivores and folivores is nonexistent. If indeed trichromacy is found in another mammal, it will refute the dogma that trichromacy is absent in non-primate mammals and, moreover, plausibly support one of the competing hypotheses for why it evolved. The Kloss gibbon, isolated for 500,000 years on the Mentawai Islands of Indonesia, is the most frugivorous ape ever observed. It may therefore model the conditions faced by our human ancestors and, like humans, may exhibit a high frequency of dichromacy. Molecular evidence on the color vision of the Kloss gibbon and a broad array of mammals with specialized diets will be obtained from DNA collected from a variety of sources, including feces and museum specimens. For the middle/long wavelength opsin(s), PCR-based gene isolation strategies will be implemented. All exons from the 2-or3 possible opsins will be entirely sequenced. For some of the non-primate species, it will be necessary to develop complete or partial genomic libraries. This study thus aims to explore the issues, implications, and evolutionary significance of color vision variation.